Medical cannabis has been widely promoted and prescribed as a potential remedy for anxiety, depression and post-traumatic stress disorder (PTSD). But a sweeping new analysis suggests this practice is not supported by science.

After examining decades of clinical data, researchers found no convincing evidence that cannabis-based treatments improve these common mental health conditions, though it may have some value for others.

The findings, published in The Lancet Psychiatry, raise new concerns about both effectiveness and safety at a time when medicinal cannabis use is rapidly expanding.

The popularity of cannabis as a “natural” remedy may be contributing to its widespread use despite limited evidence and potential risks.

The University of Sydney team conducted a systematic review and meta-analysis of the findings of 54 randomized controlled trials, a research design considered the gold standard in medical research.

The studies analyzed in the meta-analysis, described as the largest review of its kind, spanned 45 years, from 1980 to 2025 and included roughly 2,500 participants across a range of mental health and substance use disorders.

The researchers, led by Jack Wilson, a postdoctoral and research fellow at the Matilda Centre for Research in Mental Health and Substance Use at the University of Sydney, evaluated various cannabis-based products, including formulations containing THC, the psychoactive component of cannabis and CBD, a non-intoxicating compound, typically administered as capsules, oils or sprays.

The bottom line was consistent despite the diversity of products and conditions studied: Cannabis did not significantly improve symptoms of anxiety, depression or PTSD.

Clearer benefits were seen for non-psychiatric conditions, such as epilepsy, spasticity in multiple sclerosis and certain types of chronic pain.

That's notable because these are among the most common reasons people turn to medical cannabis. According to the analysis, about 27 percent of adults aged 16 to 65 in the United States and Canada report using cannabis for medical purposes and roughly half say they use it to manage mental health symptoms.

Wilson stresses that the implications go beyond lack of benefit. “Though our paper didn't specifically look at this, the routine use of medicinal cannabis could be doing more harm than good by worsening mental health outcomes, for example, a greater risk of psychotic symptoms and developing cannabis use disorder, and delaying the use of more effective treatment,” he said in a press release.

The review also explored whether cannabis might help other psychiatric or neurological conditions. There were some signals of possible benefit in areas such as insomnia, autism and Tourette's syndrome. However, the researchers emphasized that the quality of evidence in these cases was low and inconsistent, making it difficult to draw firm conclusions.

There were clearer benefits in non-psychiatric conditions: seizure disorders, spasticity in multiple sclerosis and certain types of chronic pain. But when it comes to mental health, the evidence simply doesn't measure up.

“…[T]he routine use of medicinal cannabis could be doing more harm than good by worsening mental health outcomes, for example, a greater risk of psychotic symptoms and developing cannabis use disorder, and delaying the use of more effective treatment.”

The study also examined cannabis use in people with substance use disorders, with mixed results. In individuals with cannabis dependence, certain cannabis-based treatments appeared to reduce use when combined with psychological therapy, similar in concept to how methadone is used for opioid addiction. However, in people with cocaine-use disorder, cannabis actually increased cravings suggesting it could worsen outcomes in the population.

These findings come amid growing concern from major medical organizations about the rapid expansion of cannabis prescribing, often in the absence of strong regulatory oversight. Experts warn that the popularity of cannabis as a “natural” remedy may be contributing to its widespread use despite limited evidence and potential risks.

Another complicating factor is the changing potency of cannabis products. Today's formulations often contain significantly higher levels of THC than in past decades, which may increase the risk of side effects such as dependency, cognitive impairment and psychosis, particularly in vulnerable individuals.

The findings should not be interpreted as a blanket dismissal of cannabis research, but rather as a call for more rigorous study, the authors declare. Well-designed clinical trials remain limited and the complexity of cannabis compounds makes it difficult to generalize findings across different products and populations.

For patients, the study underscores the value of first turning to proven therapies such as cognitive behavioral therapy and appropriate medications, while continuing to ask critical questions about emerging treatments. As cannabis becomes more mainstream, studies like this serve as an important reminder: popularity is not proof.